Electrical circuit interrupter



Aug. 4, I H THOMMEN 2,292,252

ELECTRICAL CIRCUIT INTERRUP'IER Filed March 15, 1941 Patented Aug. 4, 1942 UNITED STATES PATENT: orrlcs ELECTRICAL CIRCUIT INTERRUPTER Hans Tliom nen, Baden, Switzerland, 'asslgnor to Akticngesellschaft Brown, Boveri & Ole, Baden,

Switzerland, a joint-stock company Application March 13, 1941, Serial No. 883,2ld In Switzerland January 23, 1940 d Claims.

This invention relates to circuit interrupters, and particularly to circuit interrupters in which a multiple break, air blast circuit breaker and a disconnecting switchare operated in sequence to isolate the line from the source of power.

Circuit interrupters of this type preferably include resistive or reactive impedances in shunt with th several cooperating sets of circuit breaker contacts, the impedances serving to damp the arcing current and to establish a predeter- April 14, 1942.

Objects of the invention are to provide multiple break gas blast circuit breakers in which the current damping impedances in shunt with the sets of arcing contacts include resistances whose effective values vary with the voltage impressed across the resistances. An object is to provide a multiple break gas blast circuit breaker in which impedances are shunted across the several gaps. to establish a predetermined voltage gradient along the gaps, the resistances being grad- I uated in value with the larger resistances in parallel with theouter arcing contacts.

These and other objects and advantages of the invention will be apparent from the following specification when taken with the accompanying drawing in which:

Fig. 1 is a side elevation, partly in vertical section, of a circuit interrupter embodying the invention;

Fig. 2 is an enlarged vertical section through one arcing chamber and set of contacts of the circuit breaker; and

Figs. 3 and 4 are fragmentary side elevations of other fonns of the invention.

The circuit breaker comprises a plurality of arcing switch contact assemblies, identified generally by reference numerals la to "1., respectively, which are arranged in two groups and mounted on the hollow casting 2, 2' at the tops of the insulator columns 3, 3. The contact. assemblies Ia and lh have terminals 4, l, for connection'to a power line L and a branch line L, 5

(G31. Milk-M8) respectively. and the contacts of each group are in series with each otherand with a disconnecting switch comprising switch blades 5, 5' that are pivotally mounted on the respective insulator heads 2, 2', The insulator columns 3, 3 are carried by a truck or portable framework in which the hollow longitudinal members 6 serve as compressed air containers, while-the cross members of the frame are provided with an air passage l and a pilot valve 3 for admitting pressur air to the piston 9 of the blast valve ill that controls the flow of pressure air to the operating mechanism of the circuit interrupter. A large diameter pipe 9 I extends upwardly through each insulator column to connect the outlet side of the blast valve Hi to the lower end of a passage 02 that extends through the insulator head cap and opens into the base of the associated arcing switch contact assembly. A smaller pipe I3 extends upwardly through each insulator column to supply pressure air to the operating mechanism, i. e. the piston M of the disconnect switch. The control valves and air passages associated with the insulator column 3 are not shown in the drawing, but are substantial duplicates of the valves and passages illustrated in connection with the insulator column 3 and the group of switch contacts la to id.

Each switch contact assembly is substantially identical with the assembly to that is illustrated on an enlarged scale in Fig. 2. The arcing chamber for the contact assembly is formed by a cylindrical insulator M, a lower metal disk l6 upon which the insulator rests and an upper metal 1 disk It that is supported by the insulator. Each metal disk comprises upper and lower walls that are united by ribs l! and by an annular wall which forms a port i8 extending through the disk. The upper and lower plates terminate in annular flanges l9, l9, respectively, that are turned toward each other and circumferentially spaced to provide an annular outlet for the discharge of blast gases when the circuit breaker is open. A nozzle contact 20 is formed at the lower face of each metal disk It for cooperation with a pin contact 2! on a piston 22 that slides in a cylinder 23 fixed to the upper face of the next lower disk IS, The pin contact is normally held in circuit-closing position by spring 24, and the cylinder walls have openings 25 for admitting pressure gas irom the arcing chamber to force the piston downwardly to open the arcing contacts. Each of the intermediate meta1 disks l6 serves as the top wall of one arcing-chamber and as the bottom wall of th next higher chamher, and all of the arcing chambers each group are in direct communication with each other through the ports ll and thereby with the air I inlet passage I! that opens into the port l8 0! the lower contact assembly.

The several. sets or arcing switch contacts are shunted by current damping impedances 21a to 21h which provide a predetermined potential gradient along the arcing contacts when the circuit breaker is opened. According to this invention,

these impedances are formed of semi-conductive tive value of resistance becomes smaller as the.

voltageincreases and at the same time the residual current through the damping resistance is reduced to such an extent that it can easily be interrupted by a simple disconnecting switch after the circuit breaker is opened. Tests have shown that, for an equally favorable distribution of the potential over the arcing switch contacts of the circuit breaker, the damping resistance oi the voltage variant type may be or a much higher value than is permissible when the damping resistance is of the fixed type. This higher ohmic value results in a correspondingly smaller residual current to be interrupted by the disconnecting switch, thus permitting the use of disconnecting switches 01 smaller size and lower cost for a given circuit interrupter installation.

The damping impedances are preferably graduated as to magnitude, as is indicated in the drawings by the relative dimensions of the several resistors 21a to 21h. The magnitude of the resistors decreases progressively from the maximum value for resistors 21a and 21h which are bridged across the outer sets of arcing contacts, to the minimum value for resistors 21d and Tie that are bridged across the middle contacts of the series. This grading of the resistance values makes it possible to fix the voltage drop across each 01 the sets or arcing contacts, and this has proved to be of great advantage in the interruption or high voltages by gas blast circuit breakers.

The use of voltage variant resistances results in a better voltage distribution over the several arcing gaps of the circuit breaker, especially for the maximum voltages occurring in service, and the increased ohmic resistance results in satisfactory current interruption. In order to render the apparatu equally eflective for low voltages, it is expedient to connect an ordinary fixed resistance in parallel with the voltage variant resistances. As indicated in Fig. 3, the fixed resistances 28a to 28 are connected in parallel with the voltage variant resistors 21a to 21:1. inclusive. A similar set 01' fixed resistances will be connected across the second group of arcing contacts in parallel with the voltage variant resistors 21s to 21h, and the fixed resistors are graded as to magnitude in the same manner as the voltage variant resistors. The voltage variant resistors are operative at higher voltages,

while the fixed resistors are principally effective to determine the residual current when the circuit interrupter is opened under a low voltage.

As shown in Fig. 4, the damping impedance may be formed by voltage variant resistors in parallel with condensers. The impedance values may be graduated along the series or contacts as previously described. or may comprise a series of voltage variant resistors 29 and condensers 30 of substantially the same magnitude across each set 0! arcing contacts.

The circuit breaker is operated by opening the pilot valve I, either manually or automatically, to admit pressure air to the piston 9, thereby opening the blast valve III to admit pressure air to pipes 'II and i3. Pressure air enters the stacks of arcing contact assemblies and forces the pistons 22 downward to separate the contacts 20, 2|, and pressure air then escapes through the nozzle contacts 20 to extinguish the arcs that are drawn between the contacts. The'current damping resistors flu-11h carry a small residual current after the arcs are extinguished and this residual current is interrupted by the disconnect switch 5, 5'. The relative sizes of the pipes II and i3 are such that the sets of arcing contacts are opened and the arcs are extinguished before the piston I4 is displaced to open the disconnect switch.

It is to be understood that the invention is not restricted to the particular mechanisms herein illustrated for the opening of the arcing con.- tacts and that novel forms of damping resistances may be incorporated in other types 0! multiple break gas blast circuit breakers.

I claim:

1. In a circuit interrupter, the combination of a plurality .of serially connected sets of arcing contacts, each set being located in an arcing chamber, and comprising a nozzle contact, a cooperating contact, and pressure-responsive means supporting one or said contacts for movement to separate said contacts upon admission of pressure gas to the arcing chamber, of impedances shunted acrossthe respective sets 0! contacts, the impedances in shunt with the outer sets 01' contacts having a greater current-reducing effect than the impedance across an intermediate set of contacts.

2. In a circuit interrupter, the combination of a plurality oi serially connected sets of arcing contacts, each set being located in an arcing chamber, and comprising a nozzle contact, a cooperating contact, and pressure-responsive means supporting one of said contacts for movement to separate said contacts upon admission of pressure gas to the arcing chamber, of impedances shunted across the respective sets of contacts, the impedances in shunt with the outer sets or contacts having a greater current-reducing effect than the impedance across an intermediate set of contacts, said impedances each comprising a resistance that varies in magnitube with voltage, the resistance value decreasing as the voltage increases.

3. In a circuit interrupter, the combination of a plurality of serially connected sets of arcing contacts, each set being located in an arcing chamber, and comprising a nozzle contact, a

cooperating contact, and pressure-responsive means supporting one of said contacts for movement to separate said contacts upon admission of pressure gas to the'arcing chamber, of impedances shunted across the respective sets of contacts, the impedances in shunt with the outer sets of contacts having a greater current-reducing eflect than the impedance across an intermediate set of contacts, said impedances each comprising a fixed impedance in shunt with a resistance that varies in -magnitude with voltage, the resistance value decreasing as the voltage increases. 5

4. In a circuit interrupter, the combination with a plurality of serially connected series of arcing contacts, each set being located in' an 10 arcing chamber and comprising a nozzle contact,

a cooperating contact, and pressure-responsive means supporting one of said contacts for movement to separate said contacts upon the admission of a pressure gas to the arcing chamber, oi high-ohmic resistances shunted across the respective sets of contacts, each resistance having an eflfective value that decreases with voltage.

and a fixed impedance in parallel with each of said resistances.

HANS THOMMEN. 

